The relevance of energy storages for an autarky of electricity supply ...

Figure 4.3: Schematic illustration of a hydrogen fuel cell 20
(6) 2H+ + 2e- + ½ O2 à H2O
The output of fuel cells is electricity and water or water vapour. The core of the fuel
cell is a thin polymer film, which is permeable to protons when saturated with water,
but does not conduct electrons. PEM fuel cells have high power density, operate at
fairly low temperature (70 – 85° C), and thus can start up almost immediately. A
typical fuel cell produces a voltage from 0.6 V to 0.7 V, so that many cells must be
stacked together to generate sufficient power. (Rummich, 2009; Ellison, 2011)
PEM (Polymer electrolyte membrane) fuel cells have been limited to 200 KW level.
Therefore, stationary fuel cells are typically high temperature fuel cells such as
PAFC, MCFC or SOFC. Phosphoric acid fuel cells (PAFC) use liquid phosphoric
acid as electrolyte at an operating range of 150 – 200° C. Molten carbonate fuel cells
(MCFC) operate at temperatures of 600° C and above. Therefore, non-precious
metals can be used as catalysts, reducing costs. A major drawback of this type is the
durability because of the high operational temperature and the corrosive action of the
electrolyte. Solid oxide fuel cells (SOFC) are promising for stationary power
20 http://www.newmango.com/infographics/inf/fuel-cell.jpg, 17.10.2011
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